Chrysler neon 1997 Service Manual page 1321

14 - 34 FUEL SYSTEM
DESCRIPTION AND OPERATION (Continued)
FUEL PUMP RELAY—PCM OUTPUT
The fuel pump relay supplies battery voltage to the
fuel pump. A buss bar in the Power Distribution Cen-
ter (PDC) supplies voltage to the solenoid side and
contact side of the relay. The fuel pump relay power
circuit contains a 20 amp fuse between the buss bar
in the PDC and the relay. The fuse also protects the
power circuit for the Automatic Shutdown (ASD)
relay. The fuse is located in the PDC. Refer to Group
8W, Wiring Diagrams for circuit information.
The PCM controls the fuel pump relay by switch-
ing the ground path for the solenoid side of the relay
on and off. The PCM turns the ground path off when
the ignition switch is in the Off position. When the
ignition switch is in the On position, the PCM ener-
gizes the fuel pump. If the crankshaft position sensor
does not detect engine rotation, the PCM de- ener-
gizes the relay after approximately one second.
The fuel pump relay is located in the PDC. The
inside top of the PDC cover has a label showing relay
and fuse location.
DUTY CYCLE EVAP PURGE SOLENOID—PCM
OUTPUT
The duty cycle EVAP purge solenoid regulates the
rate of vapor flow from the EVAP canister to the
throttle body. The powertrain control module oper-
ates the solenoid.
During the cold start warm-up period and the hot
start time delay, the PCM does not energize the sole-
noid. When de-energized, no vapors are purged.
The engine enters closed loop operation after it
reaches a specified temperature and the programmed
time delay ends. During closed loop operation, the
PCM energizes and de-energizes the solenoid 5 to 10
times per second, depending upon operating condi-
tions. The PCM varies the vapor flow rate by chang-
ing solenoid pulse width. Pulse width is the amount
of time the solenoid is energized.
The solenoid attaches to a bracket near the front
engine mount (Fig. 22). To operate correctly, the sole-
noid must be installed with the electrical connector
on top.
ELECTRIC EGR TRANSDUCER—PCM OUTPUT
The Electric EGR Transducer contains an electri-
cally operated solenoid and a back-pressure con-
trolled vacuum transducer (Fig. 23). The PCM
operates the solenoid based on inputs from the multi-
port fuel injection system. The transducer and EGR
valve are serviced as an assembly.
When the PCM energizes the solenoid, vacuum
does not reach the transducer. Vacuum flows to the
transducer when the PCM de-energizes the solenoid.
When exhaust system back-pressure becomes high
enough, it fully closes a bleed valve in the vacuum
DUTY PURGE CYCLE SOLENOID VALVE EVAP
Fig. 22 Duty Cycle EVAP Purge Solenoid
transducer. When the PCM de-energizes the solenoid
and back-pressure closes the transducer bleed valve,
vacuum flows through the transducer to operate the
EGR valve.
De-energizing the solenoid, but not fully closing the
transducer bleed hole (because of low back-pressure),
varies the strength of the vacuum signal applied to
the EGR valve. Varying the strength of the vacuum
signal changes the amount of EGR supplied to the
engine. This provides the correct amount of exhaust
gas recirculation for different operating conditions.
The transducer and EGR valve mount to the rear
of the cylinder head (Fig. 23).
GENERATOR FIELD—PCM OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. Refer to Group
8A for Battery system information and 8C for charg-
ing system information.
IDLE AIR CONTROL MOTOR—PCM OUTPUT
The Idle Air Control (IAC) motor is mounted on the
throttle body. The PCM operates the idle air control
motor (Fig. 24). The PCM adjusts engine idle speed
through the idle air control motor to compensate for
engine load, coolant temperature or barometric pres-
sure changes.
The throttle body has an air bypass passage that
provides air for the engine during closed throttle idle.
The idle air control motor pintle protrudes into the
air bypass passage and regulates air flow through it.
The PCM adjusts engine idle speed by moving the
IAC motor pintle in and out of the bypass passage.
ENGINE MOUNT
PL